Dear Patricia,
The particular model/brand of data logger chosen is not as important as a
through understanding of what the data received from the logger is supposed
to explain.

All data loggers must be callibrated and the callibration must be
periodically checked to insure that the data are accurate.

I have been using Mac and PC loggers for more than 10 years and have
learned that callibration is a constant requirement.

There's no free lunch.

Cheers,

Jack

Jack C. Thompson
Thompson Conservation Lab
Portland, Oregon  USA

www.teleport.com/~tcl

"The lyfe so short; the craft so long to lerne."

Chaucer, _The Parlement of Foules_ 1386.